The present invention relates to a method and an apparatus for assembling an electron gun, particularly, suitable for assembling a first electrode, which has a plurality of beam apertures as opposed to one cathode used for an electron beam emission source, with a cathode structure having the cathode.
A so-called inline type electron gun is configured to emit a plurality of electron beams arranged in line in the horizontal direction.
To emit electron beams in line, the inline type electron gun includes cathodes arranged in line and a first electrode opposed to the cathodes.
The first electrode has beam apertures at positions opposed to the cathodes arranged in line.
FIG. 1A is a sectional view showing a cathode and its neighborhood of an electron gun; FIG. 1B is a plan view, seen in the direction from a first electrode to the cathode, showing the first electrode.
Referring to FIG. 1A, there is shown a cathode structure 3 including a cathode 1 and a cylindrical body 2 (hereinafter, referred to as xe2x80x9csleevexe2x80x9d). The sleeve 2 holds at its leading end portion the cathode 1 and contains a heater for heating the cathode 1.
The cathode structure 3 is held on a sleeve holder 4.
The sleeve holder 4 is fixed to a fixing member 5 made from an insulator.
While not shown, an outer peripheral portion of the fixing member 5 is mechanically fixed to an outer peripheral portion of a first electrode 6.
That is to say, the cathode structure 3 is assembled with the first electrode 6 via the fixing member 5.
In the electron gun, the first electrode 6 is integrated with a second electrode 7 adjacent thereto and other electrodes (not shown) by means of bead glass.
In general, an electron gun used for a color cathode ray tube includes three cathode structures 3 corresponding to three primary colors of light, that is, red, green, and blue.
Referring to FIG. 1B, there is shown the first electrode 6, which generally has only one aperture for allowing an electron beam to pass therethrough, that is, only one beam aperture 8 as opposed to one cathode 1.
In some cases, however, there is used an electron gun of a type including a first electrode having a plurality of beam apertures as opposed to a single cathode.
The electron gun of this type is allowed to derive a plurality of electron beams from the single cathode.
As a result, the electron gun of this type is advantageous in forming electron beams with a high current density within an electron emission ability of the single cathode and reducing a drive voltage of the cathode.
In the electron gun of this type, a plurality of beam apertures are present as opposed to the single cathode.
Accordingly, a variation in distance between each beam aperture of the first electrode and a beam emission plane of the cathode exerts an adverse effect on characteristics of the electron gun, such as a cutoff characteristic, a drive characteristic, and crossover of electron beams.
To solve such a problem, it is required to make distances between the beam apertures of the first electrode and the beam emission plane of the cathode as equal to each other as possible.
In the existing process of assembling an electron gun, a cathode holding member, including a sleeve holder and a fixing member, is assembled with a first electrode.
Subsequently, a cathode structure obtained by assembling a cathode with a sleeve is inserted in the cathode holding member and is fixed thereto by welding or the like.
In assembling the cathode structure, however, the cathode may be sometimes assembled with the sleeve in a tilting state due to a dimensional error of the cathode and a dimensional error of the sleeve.
Further, in inserting the cathode structure in the cathode holding member, the cathode may sometimes be inserted in the cathode holding member in a tilting state because a specific clearance must be ensured therebetween.
Accordingly, when the cathode structure is assembled with the first electrode, the degree of parallelization between the cathode structure and the first electrode may be sometimes degraded.
As a result, distances between the beam apertures of the first electrode and the single cathode may be uneven, causing a variation in operational characteristics of the electron gun, such as the cutoff characteristic and the drive characteristic.
An object of the present invention is to provide a method and an apparatus for assembling an electron gun including a first electrode having a plurality of beam apertures as opposed to one cathode, which are capable of equalizing distances between the beam apertures of the first electrode and a beam emission plane of the cathode.
To achieve the above object, according to a first aspect of the present invention, there is provided an electron gun assembling method used for assembling a first electrode having a plurality of beam apertures as opposed to one cathode used as an electron beam emitting source with a cathode structure having the cathode, the method including: a first step of rotating the cathode structure on its axis in a state in which the cathode structure is opposed to the first electrode, and measuring, during rotation of the cathode structure, a distance between each of the beam apertures of the first electrode and a beam emission plane of the cathode; and a second step of setting a rotational position of the cathode structure on the basis of the result measured in the first step.
In the above-described second step, preferably, the rotational position of the cathode structure is set under a condition that the maximum one of the differences between the distances from the beam apertures of the first electrode to the beam emission plane of the cathode is minimized.
According to a second aspect of the present invention, there is provided an electron gun assembling apparatus used for assembling a first electrode having a plurality of beam apertures as opposed to one cathode used as an electron beam emission source with a cathode structure having the cathode, the apparatus including: first holding means for holding the first electrode; second holding means for holding the cathode structure in a state in which the cathode structure is opposed to the first electrode held by the first holding means; rotating means for rotating the cathode structure held by the second holding means on its axis; measuring means for measuring, during rotation of the cathode structure by the rotating means, a distance between each of the beam apertures of the first electrode and a beam emission plane of the cathode; and setting means for setting a rotational position of the cathode structure on the basis of the result measured by the measuring means.
The above-described setting means preferably sets the rotational position of the cathode structure under a condition that the maximum one of the differences between the distances from the beam apertures of the first electrode to the beam emission plane of the cathode is minimized.
According to the above-described method and apparatus of the present invention, it is possible to equalize distances between beam apertures of a first electrode and a beam emission plane of a cathode, and hence to form electron beams with a high current density and reduce a drive voltage of the cathode while reducing a variation in operational characteristics such as a cutoff characteristic and a drive characteristic of the electron gun.